This invention is primarily directed for use with vehicles wherein an operator cab is mounted over the vehicle engine and is tiltable through approximately 90.degree. to expose and permit access to the engine when required. The cab is pivoted to the chassis of the vehicle at its forward end and lifting means, usually hydraulic cylinders extending between the chassis and the cab, are provided for pivoting the cab through 90.degree. and past the over-the-center or 45.degree. position. The weight of the cab tends to nest the pistons within the cylinders during the travel of the cab from a 0.degree. position to the 45.degree. position; however, once the cab passes the over-the-center or 45.degree. position, it exerts a pulling force on the pistons within the cylinders.
This invention is directed toward improvements in tilt cab hydraulic systems and particularly in the power unit and the directional control valve.
The power unit of this invention employs an air-motor-actuated hydraulic pump. Similar pumps are disclosed in assignee's U.S. Pat. No. 3,041,975, dated July 3, 1962; entitled FLUID ACTUATED HYDRAULIC POWER UNIT and U.S. Pat. NO. 3,079,900, dated Mar. 5, 1963; entitled FLUID MOTOR. The hydraulic power unit of this invention is further provided with a manual override which permits manual operation of the pump in the event of an air-power failure.
One of the major deficiencies in the prior art resides in stabilizing the tilted cab in a selected position. In most systems, even though the directional valve is in a neutral or closed position, the cab, when in positions other than the fully seated or fully tilted positions, tends to creep downwardly toward its seated or fully tilted position because of leakage within the valve to the tank or reservoir port.
Therefore, it is an objective of this invention to provide an improved hydraulic power unit for actuating the lifting cylinders in a tilt cab vehicle.
It is a further objective of this invention to provide an air-motor-actuated hydraulic pumping unit wherein the hydraulic motor is provided with a manual pumping mechanism useful as an override in the event of a pneumatic failure.
It is a further objective of this invention to provide a directional control valve for a tilt cab wherein the forces generated by the weight of the cab acting on the lifting cylinder are translated through the hydraulic system to the movable element of the valve forcing it into tight engagement with the wall of the housing of the valve surrounding the reservoir port to minimize leakage to the reservoir from the cylinders. In this way, creeping of the cab when its weight is supported by the cylinders is minimized.
It is a further objective of this invention to provide a hydraulic power system for a tilt-cab vehicle including a hydraulically actuated latch.